EP1185801B1 - Damping structure and uses - Google Patents

Description

The present invention relates to a damping structure, as well as applications of such a damping structure.

A preferred application is the use of the structure cushioning to damp vibrations of vibrating parts, such as that the main transmission box, a rotary wing aircraft, in particular a helicopter, in particular to reduce noise in the cockpit and / or in the passenger cabin of said aircraft.

It is known that, on a rotary wing aircraft, the spectra defined in the range 20 Hz to 20 kHz are the superposition of noise of different origins, likely to be grouped into two different groups according to their characteristics spectral, namely pure sounds or line noise and loud noises bandaged.

• aux fréquences caractéristiques de la chaíne cinématique de l'aéronef ;
• aux fréquences de rotation des pales des rotors (principal et arrière) et aux harmoniques de ces fréquences ;
• aux fréquences de rotation des pales des compresseurs des groupes turbomoteurs ; et/ou
• aux fréquences de rotation des pales des ventilateurs de refroidissement de la boíte de transmission principale ou de distribution d'air en cabine et/ou d'équipements électriques, ainsi qu'aux harmoniques de ces fréquences,

tandis que les bruits à large bande comprennent notamment le cas échéant :

• le bruit de couche limite se développant sur le fuselage ;
• le bruit engendré par les rotors ;
• le bruit d'écoulement des entrées d'air et des tuyères ;
• le bruit de moteur ; et/ou
• le bruit des circuits de climatisation ou de chauffage du poste de pilotage ou de la cabine des passagers.

In known manner, the pure sounds or streaks of noise appear in particular, where appropriate:

• at the characteristic frequencies of the kinematic chain of the aircraft;
• rotor rotor rotation frequencies (main and rear) and the harmonics of these frequencies;
• at rotation frequencies of the compressor blades of the turbine engines; and or
• at the rotation frequencies of the cooling fan blades of the main transmission or cabin air distribution box and / or electrical equipment, as well as the harmonics of these frequencies,

while broadband noises include, where appropriate:

• boundary layer noise developing on the fuselage;
• the noise generated by the rotors;
• the flow noise of the air inlets and nozzles;
• engine noise; and or
• the sound of air conditioning or heating circuits in the cockpit or passenger cabin.

All these noises are, of course, bothersome for the pilots and passengers.

There are various known solutions for reducing such noises to inside a rotary wing aircraft, including a helicopter.

• une réduction des vibrations de la structure et/ou d'organes mécaniques, par amortissement ou modification de la raideur ou de la masse ;
• une atténuation de la transmission acoustique, par amortissement ou modification de la raideur ou de la masse ;
• un effet de double cloison, par un espace rempli ou non par un matériau absorbant entre la structure rayonnante et des panneaux insonorisants ;
• une absorption acoustique par des matériaux fibreux ou alvéolaires ; et
• une absorption acoustique par des résonateurs d'Helmhotz.

A first known solution aims to reduce the vibration level or the radiation of noise sources and / or the fuselage. For this purpose, various physical actions can be implemented, in particular:

• a reduction of the vibrations of the structure and / or of mechanical members, by damping or modifying the stiffness or the mass;
• an attenuation of the acoustic transmission, by damping or modification of the stiffness or the mass;
• a double-wall effect, by a space filled or not by an absorbent material between the radiating structure and sound-absorbing panels;
• acoustic absorption by fibrous or cellular materials; and
• acoustic absorption by Helmhotz resonators.

The first four physical actions mentioned above allow to reduce the general level of noise in a wide range of frequencies, but they cause a significant increase in mass and very disadvantageous. Moreover, the reduction of the noise obtained then is not enough selective to eliminate the specific acoustic discomfort of emergence pure sounds.

In contrast, the fifth and last physical action mentioned above effectively reduces line noise, but only in a narrow band of frequencies, defined at design.

This first solution mentioned above and based on a passive treatment noise is therefore not totally effective, especially for noise from rays generated by vibratory excitations.

A second known solution recommends creating soundproofing passive in the form of dressing panels mounted in the station or in the passenger cabin. These panels are designed depending on the structural area to be treated and the frequency spectrum to be mitigate.

• une réduction de bruit limitée surtout en basses fréquences ;
• une augmentation de masse élevée, qui peut être de plusieurs centaines de kilogrammes pour un hélicoptère de grande taille ;
• une perte de volume non négligeable, notamment lors de l'utilisation de panneaux épais en vue d'augmenter l'effet d'absorption acoustique ; et
• des fuites acoustiques, en particulier au niveau des trous de câblage et des joints entre les panneaux.

However, this second solution also has many disadvantages and in particular:

• limited noise reduction especially at low frequencies;
• a high mass increase, which can be several hundred kilograms for a large helicopter;
• a significant loss of volume, especially when using thick panels to increase the sound absorption effect; and
• acoustic leakage, particularly at wiring holes and joints between panels.

Therefore, none of these two known and aforementioned solutions is satisfactory to reduce the annoyance caused by noise, especially the noise of lines.

One of the aims of the present invention is to propose a solution to reduce such noises.

US-A-2,417,347 discloses a shock absorber of vibration according to the preamble of claim 1.

GB-A-1,293,391 describes an antivibration support having a container filled with shot and provided with a opening, as well as a piston supported by the shot and shutter the opening.

The present invention relates for this purpose a damping structure, simple and inexpensive, with many benefits and can be used in various applications to cushion vibrations generated by vibrating sources, particularly in the to reduce noise, and this especially in a rotary wing aircraft, such as a helicopter.

For this purpose, said damping structure is remarkable, according to the invention, in that it has the features of claim 1.

Thus, when said structure is subjected to vibrations, these vibrations are transmitted to the solid bodies (in contact) of the aggregate, by through the various points of contact. At the passage of each these points of contact, some of the vibratory energy is dissipated by friction so that said vibrations are thus damped quickly and effective in said structure.

Preferably, said structure is elongated, for example under form of a bar, and said internal recess is formed longitudinally within said elongated structure.

In the context of the present invention, at least some of said solid bodies, which are for example made of synthetic material, preferably beads, are hollow, thereby reducing the weight of said solid bodies and so also the weight of the structure.

In addition, according to the invention, said solid bodies can be made in different materials (synthetic material, metal, ...) and / or have different shapes and / or sizes (diameters).

• une différence d'inertie desdits corps solides, due notamment à des tailles ou des densités différentes ; et/ou
• une différence de raideur desdits corps solides, due notamment à des matériaux différents (par exemple une matière peu rigide et intrinsèquement très amortissante ou une matière plus rigide et intrinsèquement moins amortissante),

entraínent un mouvement différent sous l'effet d'une excitation vibratoire et donc également une amplitude d'amortissement différente. Par conséquent, par un choix approprié de ces caractéristiques, on peut régler et optimiser l'amortissement mis en oeuvre par la structure d'amortissement conforme à l'invention.It will be noted that:

• a difference in inertia of said solid bodies, due in particular to different sizes or densities; and or
• a difference in stiffness of said solid bodies, due in particular to different materials (for example a material that is not rigid and intrinsically highly damping or a material that is more rigid and intrinsically less damping),

cause a different movement under the effect of vibratory excitation and therefore also a different damping amplitude. Therefore, by an appropriate choice of these characteristics, one can adjust and optimize the damping implemented by the damping structure according to the invention.

Said structure includes, in addition, at least one internal partition, solid or pierced, of any shape, in particular tubular, which is secured or not to the wall of said structure and which is arranged inside said internal recess.

This makes it possible to increase the exchange surface (friction) between the structure and the aggregate and thus also the vibration damping.

• ledit agrégat comprend de plus un liquide visqueux remplissant les espaces entre lesdits corps solides ; et/ou
• lesdits moyens pour fermer ledit évidement interne comportent une plaque rigide qui est contrainte par un élément élastique.

In addition, advantageously:

• said aggregate further comprises a viscous liquid filling the spaces between said solid bodies; and or
• said means for closing said internal recess comprises a rigid plate which is constrained by an elastic member.

• elle peut être facilement réalisée et présente un coût de fabrication faible, notamment lorsque l'évidement interne existe déjà dans la structure ;
• elle présente une masse réduite (notamment lorsque l'on utilise des corps solides creux) par rapport à certains moyens d'amortissement connus, tels que le collage de matériaux viscoélastiques, contraints ou non, sur la surface de la structure à amortir ;
• l'agrégat qu'elle comporte est protégé contre des agressions externes (feu, humidité, agents corrosifs, ...) par la structure elle-même ;
• elle est efficace sur une large bande de fréquences et ceci pour différents types de déformation (flexion, traction-compression, torsion, ...) de la structure ;
• elle n'est pas soumise à des phénomènes d'abrasion, de corrosion ou d'érosion, si on choisit un couple approprié de matériaux respectivement pour la paroi de la structure et l'agrégat ; et
• elle n'entraíne aucune modification de la durée de vie des pièces, auxquelles elle est associée.

In addition to the aforementioned advantages, the damping structure according to the invention also has the following advantages:

• it can be easily performed and has a low manufacturing cost, especially when the internal recess already exists in the structure;
• it has a reduced mass (especially when using hollow solid bodies) with respect to certain known damping means, such as the bonding of viscoelastic materials, constrained or not, on the surface of the structure to be damped;
• the aggregate it contains is protected against external aggressions (fire, humidity, corrosive agents, ...) by the structure itself;
• it is effective over a wide frequency band and this for different types of deformation (flexion, traction-compression, torsion, ...) of the structure;
• it is not subjected to phenomena of abrasion, corrosion or erosion, if one chooses a suitable pair of materials respectively for the wall of the structure and the aggregate; and
• it does not cause any change in the life of parts, which it is associated.

In a particular application, said structure can be realized in the form of a hollow pinion (of a transmission box or any other mechanical device) which is filled with said aggregate according to the invention.

The present invention also relates to a suspension system a transmission box for a rotary wing aircraft, in particular of a helicopter.

According to the invention, said suspension system which comprises a plurality of suspension bars is remarkable in that at least one said suspension bars comprises a structure such as that mentioned above.

Thus, the equivalent damping of at least one said bars, which effectively reduces, in the position of pilot and / or the cabin of the passengers of the aircraft, the noise of solidary origin which is transmitted by said processed bars.

• une bielle ;
• un moteur ;
• une boíte de vitesses ; ou
• un organe tournant, tel qu'un compresseur ou un ventilateur par exemple.

The present invention also relates to two types of damping device using the aforementioned structure, for damping the vibrations of any vibrating part, for example:

• a connecting rod;
• a motor ;
• a gearbox; or
• a rotating member, such as a compressor or a fan for example.

A first of these damping devices comprises a damping structure according to the invention which is arranged between the vibrating part and a support.

Note that the structure used is rigid and can be reported in an empty space, either directly replace a pre-existing element providing other functions, in particular mechanical or structural, such as a connecting rod for example.

A second damping device for damping vibrations a vibrating part comprising at least one hollow element, for example a suspension bar of said vibrating part, is obtained by realizing said element in the form of the aforementioned damping structure. In the scope of the present invention, the recess of this element can be either a pre-existing recess or a recess specifically practiced for the implementation of the present invention.

This second damping device has the additional advantage not to increase the clutter.

The figures of the annexed drawing will make clear how the invention can be realized. In these figures, identical references designate similar elements.

Figure 1 schematically shows a damping structure according to the invention.

Figures 2 and 3 show structures according to the invention comprising different types of solid bodies.

Figures 4 to 7 and 8 to 11 show, schematically, different embodiments of internal partitions of the structure according to the invention, respectively in longitudinal view and in plan view.

Figure 12 schematically illustrates a mechanical decomposition of the structure according to the invention.

Figure 13 shows a preferred application of the structure according to the invention, relating to the suspension of the transmission box helicopter.

The damping structure 1 according to the invention and shown schematically in Figure 1 is a mechanical element specified below which, according to the invention, has an internal recess 2, surrounded by walls 3, 4 forming an enclosure 6 and opening through an opening 7.

• un agrégat 8 qui comprend des corps solides 9 en contact et qui remplit complètement ledit évidement interne 2, bien que pour des raisons de simplification du dessin, on n'ait pas représenté les corps solides 9 dans toute l'enceinte 6 sur la figure 1 ; et
• des moyens 10 pour fermer l'évidement interne 2 et presser ledit agrégat 8 dans ledit évidement interne 2, contre lesdites parois 3 et 4.

According to the invention, said structure 1 comprises:

• an aggregate 8 which comprises solid bodies 9 in contact and which completely fills said internal recess 2, although for reasons of simplification of the drawing, the solid bodies 9 have not been represented in the entire enclosure 6 in FIG. 1 ; and
• means 10 for closing the inner recess 2 and pressing said aggregate 8 in said inner recess 2, against said walls 3 and 4.

Thus, when the structure 1 is subjected to vibrations, by example of longitudinal vibrations E or lateral vibrations F, these vibrations are transmitted by the walls 3 and 4 to the solid bodies 9 (in contact) of the aggregate 8 which is pressed, via the various points of contact. As each of these points of contact passes, a part of the vibratory energy is dissipated by friction so that said vibrations are thus damped quickly and efficiently in said structure 1, as shown in FIG. 1 with depreciation e1 and e2 for longitudinal vibrations E and depreciation f1 and f2 for lateral vibrations F.

Of course, the structure 1 can have different shapes, more or less massive. Preferably, however, it has a shape elongate, in the manner of a bar for example, and said internal recess 2 is formed longitudinally to said structure 1 inside a chamber 6 tubular, as shown in Figure 1.

• soit pleins, toute leur masse étant alors occupée par de la matière ;
• soit creux, ce qui permet de réduire le poids desdits corps solides 9 et donc également le poids de la structure 1.

In the context of the present invention, said solid bodies 9, which are made for example of synthetic material, preferably beads, may be:

• be full, all their mass being then occupied by matter;
• is hollow, which reduces the weight of said solid bodies 9 and thus also the weight of the structure 1.

• peuvent être réalisés dans des matériaux différents (polymère, céramique métallique, élastomère ...), comme cela est représenté sur la figure 2 montrant des corps solides 9A et 9B de forme et de taille identiques, mais réalisés dans des matériaux différents ; et/ou
• peuvent présenter des formes et/ou des tailles (diamètres) différentes, comme représenté sur la figure 3, notamment pour des corps 9C, 9D, 9E et 9F.

In addition, according to the invention, said solid bodies 9:

• may be made of different materials (polymer, metallic ceramic, elastomer ...), as shown in Figure 2 showing solid bodies 9A and 9B of identical shape and size, but made of different materials; and or
• may have different shapes and / or sizes (diameters), as shown in FIG. 3, in particular for bodies 9C, 9D, 9E and 9F.

• une différence d'inertie des corps solides 9A à 9F, due notamment à des tailles ou des densités différentes ; et/ou
• une différence de raideur des corps solides 9A et 9B, due notamment à des matériaux différents (par exemple une matière peu rigide et intrinsèquement très amortissante ou une matière plus rigide et intrinsèquement moins amortissante),

entraínent un mouvement différent sous l'effet d'une excitation vibratoire et donc également une amplitude d'amortissement différente. Par conséquent, par un choix approprié de ces caractéristiques, on peut régler et optimiser l'amortissement mis en oeuvre par la structure 1.It will be noted that:

• a difference in inertia of the solid bodies 9A to 9F, due in particular to different sizes or densities; and or
• a difference in stiffness of the solid bodies 9A and 9B, due in particular to different materials (for example a material that is not rigid and intrinsically highly damping, or a material that is more rigid and intrinsically less damping),

cause a different movement under the effect of vibratory excitation and therefore also a different damping amplitude. Therefore, by an appropriate choice of these characteristics, one can adjust and optimize the damping implemented by the structure 1.

In addition to said solid bodies 9, solid or hollow, the aggregate 8 can also contain a viscous liquid, for example oil, filling the free spaces in the chamber 6 between said solid bodies 9. These The latter are then immersed in a lubricating medium, which makes it possible to delay a possible heating.

• une plaque rigide 11, par exemple une plaque métallique, qui est adaptée à l'ouverture 7 de manière à pouvoir fermer, de préférence de façon étanche, l'enceinte 6 ; et
• un moyen élastique 12, de préférence un ressort, qui exerce une pression élastique sur ladite plaque rigide 11 de manière à contraindre l'agrégat 8, c'est-à-dire à le presser dans l'enceinte 6, et même éventuellement à le comprimer s'il comporte une quantité réduite de liquide ou si les corps solides 9 sont peu rigides.

Moreover, in a preferred embodiment shown in FIG. 2, the means 10 comprise:

• a rigid plate 11, for example a metal plate, which is adapted to the opening 7 so as to be able to close, preferably in a sealed manner, the enclosure 6; and
• an elastic means 12, preferably a spring, which exerts an elastic pressure on said rigid plate 11 so as to constrain the aggregate 8, that is to say to press it in the enclosure 6, and even possibly to the compress if it comprises a reduced amount of liquid or if the solid bodies 9 are not rigid.

Moreover, the damping structure 1 according to the invention has, in addition, at least one internal partition 13, which is integral with a wall 3 or 4 of the enclosure 6 of the structure 1 and which is arranged inside of the recess 2.

• dans une vue en coupe longitudinale schématique, sur les figures 4 à 7 ; et
• dans une vue en plan, sur les figures 8 à 11.

By way of illustration, various examples of partitions 13 are shown:

• in a schematic longitudinal sectional view, in Figures 4 to 7; and
• in a plan view, in Figures 8 to 11.

• peuvent être pleines (figures 4, 5, 6, 7, 8, 10 et 11 ) ou percées (figures 5, 9 et 11) ; et
• peuvent présenter des formes quelconques, par exemple planes (figures 4 à 9) ou tubulaires (figures 10 et 11). Dans ce dernier cas, les cloisons 13 peuvent présenter tout type de section transversale : circulaire, elliptique ou simplement quelconque.

As can be seen in these figures 4 to 11, the partitions 13:

• can be full (Figures 4, 5, 6, 7, 8, 10 and 11) or drilled (Figures 5, 9 and 11); and
• may have any shape, for example flat (Figures 4 to 9) or tubular (Figures 10 and 11). In the latter case, the partitions 13 may have any type of cross section: circular, elliptical or simply any.

These internal partitions 13 make it possible to increase the surface area exchange and therefore the friction surface between, on the one hand, the faces internal walls 3, 4 of the enclosure 6 and, on the other hand, the aggregate 8, which makes it possible to increase the damping of the vibrations of the structure 1.

• elle peut être facilement réalisée et présente un coût de fabrication faible, notamment lorsque l'évidement interne 2 existe déjà dans la structure 1 ;
• elle présente une masse réduite (notamment lorsque l'on utilise des corps solides 9 creux) par rapport à certains moyens d'amortissement connus, tels que des matériaux amortissants collés directement sur la surface de la structure à amortir ;
• l'agrégat 8 qu'elle comporte est protégé contre des agressions externes (feu, humidité, agents corrosifs, ...) par l'enceinte 6 ;
• elle est efficace sur une large bande de fréquences et ceci pour différents types de déformation (flexion, traction-compression, torsion, ...) de la structure 1 ;
• elle n'est pas soumise à des phénomènes d'abrasion, de corrosion ou d'érosion, si on choisit un couple approprié de matériaux respectivement pour la paroi 3, 4 de la structure 1 et pour l'agrégat 8 ; et
• elle n'entraíne aucune modification de la durée de vie des pièces, auxquelles elle est associée.

In addition to the aforementioned advantages, the structure 1 according to the invention also has the following advantages:

• it can be easily made and has a low manufacturing cost, especially when the internal recess 2 already exists in the structure 1;
• it has a reduced mass (especially when hollow solid bodies 9 are used) with respect to certain known damping means, such as damping materials bonded directly to the surface of the structure to be damped;
• the aggregate 8 that it comprises is protected against external aggressions (fire, moisture, corrosive agents, ...) by the enclosure 6;
• it is effective over a wide frequency band and this for different types of deformation (bending, traction-compression, torsion, ...) of the structure 1;
• it is not subject to phenomena of abrasion, corrosion or erosion, if a suitable pair of materials are chosen respectively for the wall 3, 4 of the structure 1 and for the aggregate 8; and
• it does not cause any change in the life of parts, which it is associated.

Hereinafter, with reference to FIG. 12, the physical effect of the filling (of the recess 2 by the aggregate 8) on the vibratory behavior of a structure 1 initially hollow (recess 2 existing, but empty).

• la flexion ;
• la traction-compression ; et
• la torsion.

Three different modes of stressing hollow structures 1 can be treated by filling with an aggregate 8, namely:

• flexion;
• traction-compression; and
• the twist.

We consider the vibratory response of a hollow structure 1 as the linear superposition of responses of second-order systems, each characterized by a natural frequency, a modal damping, a modal mass and a modal stiffness.

• MA et KA représentent respectivement la masse modale et la raideur modale réelle de la structure 1 non traitée sollicitée en flexion, longitudinal ou torsion ;
• MB représente la masse équivalente de l'agrégat 8, mise en mouvement par le couplage avec la structure 1 creuse sollicitée en flexion, longitudinal ou torsion ; et
• CB traduit le frottement interne apporté par l'agrégat 8.

At a given frequency, the structure 1 and the aggregate 8 can be replaced by the two coupled systems shown in FIG. 12, in which:

• MA and KA respectively represent the modal mass and the actual modal stiffness of the untreated structure 1 subjected to bending, longitudinal or torsion;
• MB represents the equivalent mass of the aggregate 8, set in motion by the coupling with the hollow structure 1 biased in flexion, longitudinal or torsion; and
• CB reflects the internal friction brought by the aggregate 8.

The filling of the recess 2 modifies the vibratory response of the structure 1 but does not change the F0 excitation force from excitation upstream (housing, for example, for the transmission box helicopter).

v1(t) = jω x1(t)   et   v(2)t = jω x2(t)

γ1(t) = -ω² x 1(t)   et   γ2 = -ω² x2(t).

In harmonic regime, the respective displacements in the course of time x1 (t) and x2 (t), the respective speeds v1 (t) and v2 (t) and the respective accelerations γ1 (t) and γ2 (t) satisfy for a frequency any angle ω of the amplitude excitation force F, with F0 (t) = F (ω) .sin (ωt):

v1 (t) = jω x1 (t) and v (2) t = jω x2 (t)

γ1 (t) = -ω ² x 1 (t) and γ2 = -ω ² x2 (t).

• en fonction du temps t :
  • pour la masse MA : F0(t) -KA x1 (t) - CB (v1 (t)-v2(t))   = MA γ1 (t)
  • pour la masse MB :   0   - CB (v2(t)-v1 (t))   = MB γ2(t)
• en fonction de la fréquence angulaire ω :
  • pour la masse MA : F(ω)-KAX1(ω)   -CBjω(X1(ω)-X2(ω))   = -MA ω²X1(ω)
  • pour la masse MB :   0   -CBjω(X2(ω)-X1(ω))   = -MB ω²X2(ω) avec j²=-1 et X1(ω) et X2(ω) des quantités complexes.

The sum of the forces applied (restoring forces, friction force due to the coupling with the other mass, and possibly external force F0) to each mass being equal to its inertial force, is therefore written for each mass:

• depending on the time t :
  • for the mass MA: F0 (t) -KA x1 (t) - CB (v1 (t) -v2 (t)) = MA γ1 (t)
  • for the mass MB: 0 - CB (v2 (t) -v1 (t)) = MB γ2 (t)
• according to the angular frequency ω:
  • for the mass MA: F (ω) -KAX1 (ω) -CBjω (X1 (ω) -X2 (ω)) = -MA ω ² X1 (ω)
  • for the mass MB: 0 -CBjω (X2 (ω) -X1 (ω)) = -MB ω ² X2 (ω) with j ² = -1 and X1 (ω) and X2 (ω) complex quantities.

From there, it is easy to determine (considering the frequency f in Hz) the spectrum of the amplitude acceleration / force and the spectrum of phase shift of the acceleration with respect to the force, accessible by the measure (with f = ω / 2π and fA = ωA / 2π, fA and ωA being respectively the own frequency and the proper pulsation of structure A (structure 1 no filled)).

• une forte diminution du maximum de la réponse en amplitude (définissant la fréquence de résonance du système amorti) ;
• un glissement relativement important du maximum de la réponse en amplitude vers les basses fréquences ;
• un élargissement important du spectre de réponse en amplitude ; et
• un aplatissement important de la courbe de réponse en phase.

It can be deduced that the effect of the filling (aggregate 8) of the enclosure 6 on the vibration behavior of the structure 1 results in:

• a sharp decrease in the maximum of the amplitude response (defining the resonance frequency of the damped system);
• a relatively large shift in the maximum amplitude response to the low frequencies;
• a large widening of the amplitude response spectrum; and
• a significant flattening of the phase response curve.

• αB : un coefficient sans dimension qui traduit l'efficacité réelle du remplissage ;
• δB : un angle de perte intrinsèque du matériau de remplissage, connu au préalable ; et
• mB : la masse physique apportée par le remplissage (agrégat 8).

Moreover, the coefficient CB can be expressed theoretically in the neighborhood of the eigenmode ωA by: CB = αB 2ΠfA mB tg (δB) with:

• αB: a dimensionless coefficient that reflects the actual efficiency of the filling;
• δB: an angle of intrinsic loss of the filling material, known beforehand; and
• mB: the physical mass provided by the filling (aggregate 8).

• plus l'angle de perte du matériau est élevé, plus l'amortissement équivalent est important ;
• l'amortissement équivalent est proportionnel à mB ; et
• plus la qualité du contact est élevée, meilleure est l'efficacité en amortissement du remplissage (agrégat 8).

We therefore check that:

• the higher the angle of loss of the material, the greater the equivalent damping is important;
• the equivalent depreciation is proportional to mB; and
• the higher the quality of the contact, the better the damping efficiency of the filling (aggregate 8).

The optimization of depreciation consists in increasing CB, that is to say the damping mass of the aggregate 8, which is defined by αB mB tg (δB).

• pour l'angle de perte δB :
  • le nombre de types de corps solides 9 utilisés (un seul type ou un mélange de plusieurs types) ;
  • la nature des constituants : polymère, céramique métallique ou élastomère ;
  • la viscosité du liquide de remplissage éventuellement utilisé,
• pour le coefficient d'efficacité αB :
  • l'état de surface des corps solides 9 constituant l'agrégat 8 ;
  • la pression statique de compactage engendré par les moyens 10,
• pour la masse de remplissage mB :
  • la masse volumique moyenne des corps solides 9 constituant l'agrégat 8 ;
  • le diamètre moyen des corps solides 9 constituant l'agrégat 8 ;
  • l'épaisseur de paroi des corps solides 9 constituant l'agrégat 8, si ceux-ci sont creux.

The technological parameters for increasing this damping mass are:

• for the loss angle δB:
  • the number of types of solid bodies 9 used (a single type or a mixture of several types);
  • the nature of the constituents: polymer, metallic ceramic or elastomer;
  • the viscosity of the filling liquid that may be used,
• for the coefficient of efficiency αB:
  • the surface state of the solid bodies 9 constituting the aggregate 8;
  • the static compaction pressure generated by the means 10,
• for the filling mass mB:
  • the average density of the solid bodies 9 constituting the aggregate 8;
  • the average diameter of the solid bodies 9 constituting the aggregate 8;
  • the wall thickness of the solid bodies 9 constituting the aggregate 8, if they are hollow.

Many applications are of course possible for the damping structure 1 according to the invention.

• d'une barre de liaison entre un support à isoler par rapport à des vibrations et un carter englobant des éléments tournants engendrant ces vibrations, comme on le verra plus en détail ci-après en référence à la figure 13 ; ou
• d'une suspension de moteur, de boíte de vitesses ou d'un organe tournant, tel qu'un compresseur ou un ventilateur par exemple.

In particular, said structure 1 can be used to dampen the vibrations of various types of vibrating parts. It can, thus, notably be used as part:

• a connecting bar between a support to be isolated with respect to vibrations and a housing including rotating elements generating these vibrations, as will be seen in more detail below with reference to Figure 13; or
• a motor suspension, gearbox or a rotating member, such as a compressor or a fan for example.

• être rapportées et agencées à des endroits libres entre la pièce vibrante et le support ; ou
• remplacer des éléments, par exemple des bielles, existant déjà sur la pièce ou le support ; ou
• être formées dans des éléments (creux ou non) existant déjà.

According to the invention, in order to effect the suspension of a vibrating part with respect to a support so as to isolate the latter from the vibrations of said vibrating part, one or more structures 1, in particular in bar form, can:

• be reported and arranged at free places between the vibrating part and the support; or
• replacing elements, for example connecting rods, already existing on the part or the support; or
• be formed in elements (hollow or not) already existing.

The last two solutions have the added advantage of not not increase the clutter.

• du bruit d'engrènement ou de roulement provenant des boítes de transmission ; et/ou
• du bruit d'engrènement ou de roulement de boítiers accessoires (pompes de lubrification, entraínement de groupes de ventilation, climatisation ...),

bruits qui sont très gênants en cabine, à la fois pour les pilotes et les passagers.Preferred applications of the damping structure 1 relate to the reduction of noise generating vibrations, on a rotary wing aircraft, in particular a helicopter, and in particular the reduction:

• meshing or rolling noise from transmission boxes; and or
• meshing noise or rolling accessory housings (lubrication pumps, drive ventilation units, air conditioning ...),

noises that are very annoying in the cabin, for both pilots and passengers.

The particular application of the invention, shown in FIG. 13, is intended to increase the damping of suspension bars 15 a suspension system of the main transmission box BTP (connected to the mast 16 of the rotor of advance and levitation) of a helicopter He, suspension bars 15 which are arranged on the fuselage 17 of the helicopter Hey.

To do this, these suspension bars 15 each comprise a damping structure 1 according to the invention, as can be see him for one of these bars 15 which is partially torn off the figure 13.

This is done with the aim of reducing in the cabin the noise of solid origin transmitted by the bars 15, that is to say the vibratory energy transmitted by said bars 15, translated by an expression | H (f) || γbarre | ² (f) specified below.

In general, we can consider that the sound pressure spectrum in the cabin of the helicopter He, noted Pcab (f), verifies the following quadratic relationship: PCAB 2 (F) = | T (f) || Pdirect | 2 (F) + | H (f) || γbarre | 2 (F) + | Q (f) || γstructure | 2 (F)

Indeed, this summation of amplitudes squared reflects the balance sheet energy transfers for meshing noise at frequencies above 500 Hz. There is no need to take into account the phase between cabin pressure and direct pressure or accelerations of the structure (fuselage) of the helicopter He, given the large number acoustic modes present in the cabin at these frequencies.

• le terme |T(f)||Pdirect|²(f) représente la pression acoustique quadratique en cabine, due uniquement au bruit rayonné directement par la boíte de transmission principale BTP de l'hélicoptère Hé. |T(f)| représente le module du coefficient de transmission acoustique (sans dimension) du bruit rayonné par voie aérienne d'amplitude Pdirect jusqu'à la cabine ;
• le terme |H(f)||γbarre|²(f) représente la pression acoustique en cabine, due uniquement au bruit rayonné en cabine par la structure (partie de fuselage 17) excitée par les vibrations des attaches des barres 15. |H(f)| représente l'efficacité de rayonnement acoustique en cabine des vibrations de cette partie du fuselage ;
• le terme |Q(f)||γstructure|²(f) représente la pression acoustique quadratique en cabine, due uniquement au bruit rayonné en cabine par le reste du fuselage qui n'est pas excité par les vibrations des attaches des barres 15, mais par le fond de la boíte de transmission BTP par exemple. |Q(f)| représente le module du coefficient de rayonnement acoustique en cabine de cette dernière partie de fuselage.

It will be noted that:

• the term | T (f) || Pdirect | ² (f) represents the cabin sound pressure due solely to the noise radiated directly from the main transmission unit BTP of the Hel helicopter. | T (f) | represents the modulus of acoustic transmission coefficient (dimensionless) of noise radiated by air amplitude Pdirect up to the cabin;
• the term | H (f) || γbarre | ² (f) represents the acoustic pressure in the cabin, due solely to the noise radiated in the cabin by the structure (fuselage portion 17) excited by the vibrations of the fasteners of the bars 15. | H (f) | represents the acoustic radiation efficiency in the vibration cabin of this part of the fuselage;
• the term | Q (f) || γstructure | ² (f) represents the square sound pressure in the cabin, due solely to the noise radiated in the cabin by the rest of the fuselage which is not excited by the vibrations of the fasteners of the bars 15, but by the bottom of the transmission box BTP by example. | Q (f) | represents the modulus of acoustic radiation coefficient in the cabin of this last fuselage part.

From the foregoing, it appears that the noise reduction in the cabin will be significant at meshing frequencies, for which the following relationship is verified in the absence of treatment: | H (f) || γbarre | 2 (F) >> | T (f) || Pdirect | 2 (F) + | Q (f) || γstructure | 2 (F).

Claims (17)

1. A damping structure (1), having an inner cavity (2) surrounded by walls (3, 4) forming an enclosure (6) and opening at an aperture (7), and including an aggregate (8) which comprises at least firm bodies (9) in contact with one another, the structure further including means (10, 11) adapted to the aperture (7), for closing the inner cavity (2), and at least one inner partition (13) which is arranged inside the said inner cavity (2), the structure being characterised in that the aggregate (8) fills the said inner cavity (2), and in that at least some of the said firm bodies (9) are hollow.
2. A damping structure according to Claim 1, characterised in that it further includes a resilient means (12) which exerts a pressure on the said aggregate (8) in order to compress it.
3. A damping structure according to Claim 1 or 2, characterised in that the said inner partition (13) is pierced at least in certain parts.
4. A damping structure according to any one of Claims 1 to 3, characterised in that the means for closing the cavity include a rigid plate (11).
5. A damping structure according to Claims 2 and 4, characterised in that the resilient means (12) exerts a resilient pressure on the said rigid plate (11) such that the said aggregate (8) is compressed.
6. A damping structure according to any one of the preceding claims, characterised in that it is elongated, and in that the said inner cavity (2) is formed longitudinally within the said structure (1).
7. A damping structure according to any one of the preceding claims, characterised in that some of the said firm bodies (9) are solid.
8. A damping structure according to any one of the preceding claims, characterised in that the said aggregate (8) includes firm bodies (9A, 9B) made of different materials.
9. A damping structure according to any one of the preceding claims, characterised in that the said aggregate (8) includes firm bodies (9C, 9D, 9E, 9F) of different shapes.
10. A damping structure according to any one of the preceding claims, characterised in that the said aggregate (8) includes firm bodies (9C, 9D, 9E, 9F) of different sizes.
11. A damping structure according to any one of the preceding claims, characterised in that the said inner partition (13) is tubular in shape.
12. A damping structure according to any one of the preceding claims, characterised in that the said aggregate (8) completely fills the said cavity (2), and in that the enclosure (6) is rigid.
13. A damping structure according to any one of the preceding claims, characterised in that the said aggregate (8) further comprises a viscous liquid filling the spaces between the said firm bodies (9).
14. A damping structure according to any one of the preceding claims, characterised in that it takes the form of a pinion.
15. A system of suspension for a gearbox of a rotor aircraft, in particular a helicopter, the said system of suspension comprising a plurality of suspension rods (15), characterised in that at least one of the said suspension rods (15) includes a damping structure according to any one of Claims 1 to 13.
16. A device for damping the vibrations of a vibrating part mounted on a support, characterised in that it includes a damping structure (1) as specified in any one of Claims 1 to 14, which is arranged between the said vibrating part (principal gearbox BTP) and the said support (17).
17. A device for damping the vibrations of a vibrating part including at least one hollow element, characterised in that the said hollow element (15) takes the form of a damping structure (1) as specified in any one of Claims 1 to 14.

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